It has been known for a long time that escalators and moving walkways must be stopped when defects arise in the region of the so-called comb plate at the entry or exit. Comb plates typically carry a plurality of comb segments which are distributed across the width of the escalator or of the moving walkway and which have teeth or forks which mesh with channels or grooves in the escalator steps or moving walkway panels.
Manufacturers of escalators and moving walkways of this type do pay attention to the lateral free play of the forks in relation to the webs of the escalator steps or moving walkway panels being sufficiently dimensioned such that there is in the normal case no contact—and thus typically no tooth breakage. However, when the escalator step, or else the respective comb segment, is subjected to excessive lateral offset on account of an external influence, the respective web impacts a tooth, which inevitably leads to tooth breakage.
Tooth breakage implies a risk for the passengers of the escalator or of the moving walkway, such that a stoppage of the escalator or of the moving walkway has to be automatically initiated.
On account of the tooth breakage a significant force is exerted on the respective tooth segment, leading to the dislocation of the latter. The dislocation may take place vertically or in a substantially horizontal manner or else obliquely, depending on the angle of impact of the tooth on the web, the dislocation typically being reversible.
In order for tooth breakage to be identified and the required measures to be initiated, measures in the form of providing safety installations which are to detect the movement of the comb segment and/or of the comb plate and trigger an alarm signal have been known for a long time.
An early example thereof is DE 680 845, according to which a belt-shaped safety member is said to extend transversely across the width of the escalator. This safety member is guided in a groove or bore which is just above the surface of the escalator step and which extends through the comb segments or, more precisely, through the actual teeth, in a transverse manner across the width of the escalator. A light barrier or a lacerable belt may also be employed as a safety member, and raising of the escalator step beyond a permissible dimension would also lead to the safety installation being triggered.
Furthermore, DE 299 07 184 A1 discloses an escalator and a moving walkway wherein the comb segments there have on the teeth a line which is said to be interrupted in the case of tooth breakage. Whilst this solution is fundamentally very safe, it does require, however, for the line to be renovated in the case of the breakage of a tooth and the replacement of the respective comb segment which is thus required. In contrast thereto, the method disclosed in DE 299 07 184 A1 for example has the disadvantage that the line to be interrupted is accessible from the outside and thus may also be interrupted by events which do not make safety-related disabling of the steps necessary.
Indeed, a glass-fibre conductor may also be used as a line; but said glass-fibre conductor would also have to be renovated in the potential case of a breakdown on account of tooth breakage, this likewise leading to additional costs.